Firstly, there is the general recognition, always patent to ourselves, that by far the most drastic, economical, and effective way of securing control is to destroy the enemy’s means of interfering with it.  In our own service this “overthrow” idea always tended to assert itself so strongly, that occasionally the means became for a time more important than the end; that is to say, circumstances were such that on occasions it was considered advisable to sacrifice the exercise of control for a time in order quickly and permanently to deprive the enemy of all means of interference.  When there was reasonable hope of the enemy risking a decision this consideration tended to override all others; but when, as in Nelson’s case in the Mediterranean, the hope was small, the exercise of control tended to take the paramount place.

The second complexity arose from the fact that however strong might be our battleship cover, it is impossible for it absolutely to secure cruiser control from disturbance by sporadic attack.  Isolated heavy ships, taking advantage of the chances of the sea, could elude even the strictest blockade, and one such ship, if she succeeded in getting upon a line of communication, might paralyse the operations of a number of weaker units.  They must either run or concentrate, and in either case the control was broken.  If it were a squadron of heavy ships that caused the disturbance, the practice was to detach against it a division of the covering battle-fleet.  But it was obviously highly inconvenient and contrary to the whole idea on which the constitution of the fleet was based to allow every slight danger to cruiser control to loosen the cohesion of the main fleet.

It was necessary, then, to give cruiser lines some power of resistance.  This necessity once admitted, there seemed no point at which you could stop increasing the fighting power of your cruisers, and sooner or later, unless some means of checking the process were found, the distinction between cruisers and battleships would practically disappear.  Such a means was found in what may be called the “Intermediate” ship.  Frigates did indeed continue to increase in size and fighting power throughout the remainder of the sailing era, but it was not only in this manner that the power of resistance was gained.  The evil results of the movement were checked by the introduction of a supporting ship, midway between frigates and true ships-of-the-line.  Sometimes classed as a battleship, and taking her place in the line, the 50-gun ship came to be essentially a type for stiffening cruiser squadrons.  They most commonly appear as the flagships of cruiser commodores, or stationed in terminal waters or at focal points where sporadic raids were likely to fall and be most destructive.  The strategical effect of the presence of such a vessel in a cruiser line was to give the whole line in some degree the strength of the intermediate ship; for any hostile cruiser endeavouring to disturb the line was liable to have to deal with the supporting ship, while if a frigate and a 50-gun ship got together they were a match even for a small ship-of-the-line.